This invention relates to an adapter and method for modifying printed circuit boards. More particularly, this invention relates to an adapter and method suited for modifying printed circuit board assemblies having a land grid array (LGA) device and an interposer socket having compliant contacts for providing electrical coupling between pads of the LGA device and pads of a circuit board to which the LGA device is to be mounted.
Manufacturers that are involved in the design and fabrication of printed circuit boards may, under some circumstances, find it necessary to modify newly designed printed circuit boards in order to implement engineering improvements. Over the years, various rework techniques have been proposed for use with printed circuit boards.
These proposed techniques are often specialized in that they are suited for use with particular types of printed circuit boards and circuit board components. Accordingly, some of the techniques proposed in the past are appropriate for use with certain component types but may be ineffective for use with other types of components.
For example, referring generally to FIGS. 1 and 2, an exemplary printed circuit board modification procedure will now be described. Referring first to FIG. 1, a circuit board assembly 10 includes an electronic device 12 mounted to a circuit board 14. Circuit board 14 includes a plurality of pads 16, and surface traces connect the pads 16 to a plurality of vias 18. Electronic device 12 is provided with a plurality of pins or leads 28, which provide for electrical coupling with selected pads 16 on the circuit board 14.
A modification can be made to such a printed circuit board in two stages. The first stage can be considered xe2x80x9cpin isolation,xe2x80x9d wherein a pin of an electronic device is isolated from a circuit on the printed circuit board. This stage is illustrated in FIG. 1, wherein a surface trace cut isolates a surface mount pad from a via hole that is connected to the rest of the circuit More specifically, a surface trace cut 20 is made in order to isolate a surface mount pad 16 from a via 18. The surface trace cut 20 therefore provides an accessible connection 22 to which a modification can be made (as shown in FIG. 2). A surface trace cut 24, however, is hidden beneath electronic device 12. Accordingly, surface trace cut 24 provides an inaccessible connection 26.
Referring now to FIG. 2, the second stage is illustrated. In this stage, which can be considered a xe2x80x9ccircuit re-connectionxe2x80x9d stage, a pin of an electronic device is connected to another circuit using a wire. Specifically, a wire 30 is connected to a pin or lead 28 of electronic device 12 by means of a soldered connection 32. An opposite end 34 of wire 30 is provided for connection to an external circuit. Similarly, a second wire 36 is connected to another pin or lead of electronic device 12 at a soldered connection 38. An opposite end of wire 36 is provided with an end 40 for connection to an external circuit.
Pin isolation for an electronic device such as device 12 is usually a straight forward procedure and the manner m which circuit re-connection is made depends primarily on the accessibility of the surface trace being cut or on the accessibility of the pin that is to be isolated. For example, if a trace is not readily accessible (e.g., for making the surface trace cut 24 illustrated in FIG. 1), then an electronic device such as device 12 is first removed from the printed circuit board so that the trace can be accessed, and the device can be subsequently reinstalled. Nevertheless, an inaccessible connection such as connection 26 can be overcome by connecting a wire directly to the exposed lead of the device such as at soldered connection 38.
It will be appreciated, therefore, that the modification procedure illustrated in FIGS. 1 and 2 is suitable for use with devices such as device 12 that have pin-type leads, but that the modification will not be adequate for use with electronic devices of the type where the pins or leads of the device are not accessible. Accordingly, there remains a need for an adapter and method for use with electronic devices which have leads that are not easily accessible. More specifically, there remains a need for an adapter and method that can be used with land grid array (LGA) devices.
This invention provides an adapter for use with a land grid array (LGA) device and an interposer socket having compliant contacts for providing electrical coupling between pads on the LGA device and pads on a circuit board to which the LGA device is to be mounted. The adapter includes a flexible substrate configured to positioned adjacent the interposer socket. The adapter also includes a plurality of conductors extending through the flexible substrate, and the conductors include pads adjacent facing surfaces of the flexible substrate. The flexible substrate is configured to flex in reaction to forces exerted by the compliant contacts of the interposer socket. The flexibility of the substrate facilitates contact between the pads of the conductors adjacent one surface of the flexible substrate with the compliant contacts of the interposer socket. The flexibility of the substrate also facilitates contact between the pads of the conductors adjacent an opposite surface of the flexible substrate with pads of the circuit board (when the adapter is positioned between the interposer socket and the circuit board) or with pads of the LGA device (when the adapter is positioned between the interposer socket and the LGA device).
According to another aspect of this invention, a circuit board assembly is provided. The assembly includes a circuit board having a plurality of pads and a land grid array (LGA) device also having a plurality of pads. The assembly also includes an interposer socket positioned to extend in a space between the circuit board and the LGA device and having a plurality of compliant contacts positioned for contact with the pads of the LGA device or the pads of the circuit board. The assembly further includes an adapter positioned to extend in a space between the interposer socket and the circuit board or, alternatively, in a space between the interposer socket and the LGA device. The adapter comprises a flexible substrate positioned adjacent the interposer socket and a plurality of conductors extending through the flexible substrate. The conductors include pads adjacent facing surfaces of the flexible substrate. Pads adjacent one facing surface of the flexible substrate are positioned for electrical contact with the compliant contacts of the interposer socket. The flexible substrate of the adapter is configured to flex in reaction to forces exerted by the compliant contacts of the interposer socket. Accordingly, electrical contact is maintained between the pads of the circuit board and the pads of the adapter when the adapter is positioned between the interposer socket and the circuit board. Alternatively, electrical contact is maintained between the pads of the LGA device and the pads of the adapter when the adapter is positioned between the interposer socket and the LGA device.
According to yet another aspect of this invention, a method is provided for adapting a circuit board assembly having a land grid array (LGA) device and an interposer socket extending between the LGA device and a circuit board. An adapter having a flexible substrate and conductors extending therethrough is provided. The adapter is positioned between the interposer socket and the circuit board or, alternatively, between the interposer socket and the LGA device. Selected electrical coupling is provided through the adapter between the compliant contacts of the interposer socket and pads on the circuit board (when the adapter is positioned between the interposer socket and the circuit board) or through the adapter between the compliant contacts of the interposer socket and pads on the LGA device (when the adapter is positioned between the interposer socket and the LGA device). Pressure is applied to urge the LGA device and the circuit board toward one another, and the compliant contacts of the interposer socket are electrically coupled to the conductors of the adapter. Also, the conductors of the adapter are electrically coupled to the pads of the circuit board when the adapter is positioned between the interposer socket and the circuit board. Alternatively, the conductors of the adapter are electrically coupled to the pads of the LGA device when the adapter is positioned between the interposer socket and the LGA device.